High‐Energy Gamma Rays from the Massive Black Hole in the Galactic Center

Accreting black holes are believed to be sites of possible particleacceleration with favorable conditions also for effective gamma-ray production.However, because of photon-photon pair production, only low energy (MeV)gamma-rays can escape these compact objects with typically very largecompactness parameter, given that in most cases the accretion disks within 10Schwarzschild radii radiate with a power exceeding 10 percent of the Eddingtonluminosity. Therefore, the high-energy gamma-ray emission of these objects(both stellar mass and supermassive BHs) is generally suppressed, andconsequently the unique information on possible particle acceleration processnear the event horizon of the BH is essentially lost. Fortunately, this is notthe case for the super-massive BH located at the dynamical center of our Galaxy(Sgr A*) which, thanks to its extraordinary low bolometric luminosity istransparent fo gamma-rays up to very high energies, about 10 TeV. We discussdifferent scenarios of gamma-ray production in Sgr A* and show that for areasonable set of parameters one can expect detectable gamma-ray fluxes of bothhadronic and electronic origin. Some of these scenarios are applicable not onlyfor the TeV gamma-ray emission recently reported from the direction of GalacticCenter, but may have broader implications relevant to highly variablenonthermal emission of Sgr A* in radio, IR and X-ray bands.Comment: submitted to Astrophysical Journa